Flame-resistant thermoplastic moulding materials with improved processing behavior

ABSTRACT

Flame-retardant thermoplastic molding materials containing 
     A) at least one polyphenylene ether and 
     B) at least one vinyl aromatic polymer, comprise 
     C) as a flameproofing agent, a mixture of 
     C 1 ) at least one oligophosphonate or oligophosphate compound 
     and 
     C 2 ) at least one phosphine oxide.

The present invention relates to flame-retardant thermoplastic moldingmaterials having improved processing behavior, the use of the novelthermoplastic molding materials for the production of fibers, films andmoldings, and the fibers, films and moldings produced using thesemolding materials.

Polymer blends comprising polyphenylene ether (PPE) and styrene polymersare disclosed, for example, in U.S. Pat. Nos. 3,383,435; 4,128,602 and4,128,603. Such molding materials are suitable for 15 the production ofshaped articles which have better heat distortion resistance thanhigh-impact polystyrenes (HIPS) which are not mixed with polyphenyleneethers. A detailed description of the properties of these polymer blendsalso appears in L.Bottenbruch, “Technische Polymer-Blends”, KunststoffHandbuch 20 3/2, Hanser Verlag, Munich, 1993.

An important advantage of the polymer blends comprising polyphenyleneethers and styrene polymers is that, by adding halogen-freeflameproofing agents, in particular phosphorus-containing compounds, itis possible to prepare molding materials which are flame-retardant andare therefore used for many electrical applications. In particular,testing of the flame-retardance according to UL 94 (in J.Troitzsch,“International Plastics Flammability Handbook”, page 346 et seq., HanserVerlag, Munich, 1990) is decisive for use in the electrical sector. Inthis test, a flame is applied several times to vertically fastened testspecimens. The test specimen heats up to a very great extent, leading inmany cases to the dripping of flaming polymer material which ignites thecotton wool positioned under the rod. This undesirable behavior isobserved in particular when large amounts of flameproofing agent have tobe used to achieve short combustion times.

There is therefore a need for novel, highly effective flameproofingcombinations which permit a reduction in the amount of flameproofingagent.

The literature discloses a number of examples where mixtures ofdifferent flameproofing agents have led to improvements in theproperties of thermoplastic molding materials. For example, JP 57207641describes PPE/HIPS blends, in which a mixture of resorcinol diphenylphosphate (RDP) and triphenyl phosphate (TPPA) was used. GermanLaid-Open Application DE-OS 32 34 033 discloses PPE/HIPS blends whichcontains synergistic mixtures of phosphine oxides and monophosphates asflameproofing agents. This flameproofing combination permits a reductionin the amount of flameproofing agent, having an advantageous effect onthe mechanical properties of the molding materials produced therefrom.However, these molding materials have disadvantages with regard to theprocessing behavior.

Furthermore, mixtures of phosphorus-containing compounds with nitrogencompounds have been described as flameproofing combinations. Forexample, JP 05025341 describes a phosphate/melamine mixture whichcomprises red phosphorus as a further component. Combinations ofphosphorus-containing compounds with nitrogen and sulfur compounds aredescribed, for example, in EP 0 496 120. Whereas the first combinationleads to an improvement of the fire behavior, the second mixture claimedin EP 0 496 120 also has advantages with regard to coating of the mold.However, such mixtures have disadvantages with respect to toughness.

EP 0 090 523 describes polphenylene ether resins which contain ahydroxyl- and carboxyl-substituted ethylene polymer for improving thetoughness of the molding materials. Unsubstituted or substitutedtriphenyl phosphate is mentioned as a possible flameproofing agent.

EP 0 538 950 describes polymer compositions having improved flameproofproperties, the composition comprising, in addition to a copolymergrafted onto rubber, a polymer having hydroxystyrene units. Mono-, di-and oligomeric polyphosphates and metal and metalloid salts of organicphosphoric acid derivatives are mentioned as possible flameproofingagents.

It is an object of the present invention to provide an effectiveflameproofing combination for thermoplastic molding materials,inparticular for thermoplastic molding materials based on polyphenyleneethers and vinyl aromatic polymers, such as HIPS, which combinationpermits optimization of the properties of the molding material withregard to fire behavior, mechanical properties and processing behavior.

We have found, surprisingly, that this object is achieved with the useof a combination of oligophosphorus compounds and phosphine oxides.

The present invention therefore relates to flame-retardant thermoplasticmolding materials based on

A) at least one polyphenylene ether and

B) at least one vinyl aromatic polymer, which comprises,

C) as a flameproofing agent, a mixture of

C₁) at least one oligophosphorus compound of the general formula (I)and/or (II)

where

R¹ and R⁴, independently of one another, are each unsubstituted orsubstituted alkyl or aryl,

R² and R³, independently of one another, are each unsubstituted orsubstituted alkyl, aryl, alkoxy or aryloxy,

R⁵ is alkylene, —SO₂—, —CO—, —N═N— or —(R⁶)P(O)—, where R⁶ isunsubstituted or substituted alkyl, aryl or alkylaryl, and

n and p, independently of one another, are each from 1.0 to 30, and

C₂) at least one phosphine oxide of the general formula (III)

where R⁷, R⁸ and R⁹, independently of one another, are each hydrogen orunsubstituted or substituted alkyl, aryl, alkylaryl or cycloalkyl of upto 40 carbon atoms.

Suitable substituents in compounds of the formulae (I), (II) and (III)are cyano, hydroxyl, C₁₋₁₄-alkyl and halogen, such as F, Cl, Br and J.

Preferred alkyl radicals are C₁-C₂₀-alkyl, in particular C₁-C₁₂-alkyl,e.g. methyl, ethyl, n-propyl, n-butyl, neopentyl, n-hexyl, n-octyl,n-nonyl, n-dodecyl, 2-ethylhexyl, 3,5,5-trimethylhexyl and substitutedalkyl radicals, e.g. 5 cyanoethyl.

Preferred aryl radicals are phenyl and naphthyl as well as mono- orpolysubstituted radicals, such as tolyl, xylyl, mesityl and cresyl.

Preferred alkylaryl radicals are C₁-C₂₀-alkylaryl, in particularC₁-C₁₂-alkylaryl, radicals, the alkyl moiety and aryl moiety being asdefined above.

Preferred cycloalkyl groups include C₃-C₁₀-cycloalkyl, such ascyclobutyl, cyclopentyl, cyclohexyl and cycloheptyl.

Preferred alkoxy radicals are C₁-C₂₀-alkoxy radicals, the C₁-C₂₀-alkylmoiety being as defined above.

Preferred aryloxy radicals are those in which the aryl moiety is asdefined above.

Preferred alkylene radicals are C₁-C₆-alkylene, such as methylene,ethylene, propylene and hexylene.

The novel molding materials contain the flameproofing combination,preferably in an amount of from about 1 to about 20% by weight, based onthe total weight of the molding material.

If necessary, a polymeric hydroxy compound may additionally be presentin an amount which improves the fire behavior.

According to a preferred embodiment of the invention, a molding materialis provided, containing

A) from about 5 to about 98% by weight of polyphenylene ethers,

B) from about 1 to about 94% by weight of styrene polymers,

C) from about 1 to about 20% by weight of flameproofing combinationwhich comprises

from about 5 to about 95% by weight of at least one phosphorus compoundof the above general formula (I) and/or (II) as component C₁

and

from about 5 to about 95% by weight of a phosphine oxide of the abovegeneral formula (III) as component C₂,

D) from about 0 to about 50% by weight of an impact modifier,

E) from about 0 to about 10% by weight of a hydroxyl-carrying polymer

and

F) from about 0 to about 60% by weight of conventional 10 additives.

Here, the stated contents of C₁ and C₂ are each based on the totalweight of the flameproofing combination.

A flameproofing combination which contains a mixture of resorcinoldiphenyl phosphate and/or hydroquinone diphenyl phosphate withtriphenylphosphine oxide is particularly preferred.

Phosphate and phosphine oxide are preferably present in a molar ratio offrom about 1:9 to about 9:1.

The polyphenylene ethers (component A) contained in the novel moldingmaterials are known per se. The polyphenylene ethers are contained inthe novel molding materials in an amount of from about 5 to about 98,preferably from about 15 to about 88, in particular from about 20 toabout 82.5% by weight, based on the total weight of the moldingmaterial.

These are compounds based on substituted, in particular disubstituted,polyphenylene ethers, the ether oxygen of one unit being bonded to thebenzene nucleus of the neighboring unit. 35 Polyphenylene etherssubstituted in the 2 and/or 6 position relative to the oxygen atom arepreferably used. Examples of substituents are halogen, such as chlorineand bromine, long-chain alkyl of up to 20 carbon atoms such as lauryland stearyl, and short-chain alkyl of 1 to 4 carbon atoms whichpreferably has no a tertiary hydrogen atom, e.g. methyl, ethyl, propyland butyl. The alkyl radicals may in turn be monosubstituted orpolysubstituted by halogen, such as chlorine or bromine, or by hydroxyl.Further examples of possible substituents are alkoxy, preferably of 1 to4 carbon atoms, and phenyl which is monosubstituted or polysubstitutedby halogen and/or C₁₋₄-alkyl according to the above definition.Copolymers of different phenols, for example copolymers of2,6-dimethylphenol and 2,3,6-trimethylphenol, are also suitable. Ofcourse, mixtures of polyphenylene ethers may also be used.

Examples of polyphenylene ethers which can be used according to theinvention are:

poly(2,6-dilauryl-1,4-phenylene ether),

poly(2,6-diphenyl-1,4-phenylene ether),

poly(2,6-dimethoxy-1,4-phenylene ether),

poly(2,6-diethoxy-1,4-phenylene ether),

poly(2-methoxy-6-ethoxy-1,4-phenylene ether),

poly(2-ethyl-6-stearyloxy-1,4-phenylene ether),

poly(2,6-dichloro-1,4-phenylene ether),

poly(2-methyl-6-phenyl-1,4-phenylene ether),

poly(2,6-dibenzyl-1,4-phenylene ether),

poly(2-ethoxy-1,4-phenylene ether),

poly(2-chloro-1,4-phenylene ether),

poly(2,5-dibromo-1,4-phenylene ether).

Preferred polyphenylene ethers are those which have alkyl radicalsubstituents with 1 to 4 carbon atoms, e.g.:

poly(2,6-dimethyl-1,4-phenylene ether),

poly(2,6-diethyl-1,4-phenylene ether),

poly(2-methyl-6-ethyl-1,4-phenylene ether),

poly(2-methyl-6-propyl-1,4-phenylene ether),

poly(2,6-dipropyl-1,4-phenylene ether) and

poly(2-ethyl-6-propyl-1,4-phenylene ether).

For the purpose of the present invention polyphenylene ethers are alsoto be understood as meaning those which are modified with monomers, suchas fumaric acid, maleic acid, maleic anhydride or citric acid.

Such polyphenylene ethers are described, inter alia, in WO 87/00540.

In particular, polyphenylene ethers which have a weight averagemolecular weight M_(w) of from about 8 000 to 70 000, preferably fromabout 12 000 to 50 000, in particular from about 20 000 to 45 000, areused in the compositions.

This corresponds to a limiting viscosity of about 0.18 to 0.7,preferably from about 0.25 to 0.55, in particular from about 0.30 to0.50, dl/g, measured in chloroform at 25° C.

The molecular weight distribution is determined in general by means ofgel permeation chromatography (0.8×50 cm Shodex separation columns oftype A 803, A 804 and A 805 with THF as eluant at room temperature). Thepolyphenylene ether samples are dissolved in THF under pressure at 110°C., 0.16 ml of 0.25% strength by weight solution being injected.

Detection is carried out in general with a UV detector. The columns werecalibrated with polyphenylene ether samples whose absolute molecularweight distributions were determined by a GPC/laser light scatteringcombination.

The vinylaromatic polymer (component B) is contained in the novelmolding materials in amounts of from about 1 to about 94, preferablyfrom about 10 to about 83, in particular from about 15 to about 77.5,%by weight, based on the total weight of the molding material. Thecomponent B is a vinyl aromatic polymer which is preferably compatiblewith the polyphenylene ether used. Both homo- and copolymers of vinylaromatic monomers of 8 to 12 carbon atoms, which are prepared in thepresence of a rubber, are suitable. The rubber content is from about 5to 25, preferably from about 8 to 17,% by weight.

High-impact polystyrenes or copolymers of styrene and other vinyl 30aromatic compounds are particularly suitable. Such high impactpolystyrenes are generally known as HIPS and for the most part arecommercially available. They have a viscosity number (VN) of the hardmatrix of from about 50 to about 130, preferably from about 60 to about90, ml/g (0.5% strength in toluene at 23° C.).

Suitable monovinyl aromatic compounds are styrenes alkylated on thenucleus or side chain. Examples are chlorostyrene, o-methylstyrene,p-methylstyrene, vinyltoluene and p-tert-butylstyrene. However, styrenealone is preferably used.

The homopolymers are generally prepared by the known mass, solution andsuspension methods (cf. Ullmanns Enzyklopadie der techn. Chemie, Volume19, pages 265 to 272, Verlag Chemie, Weinheim 1980). The homopolymersmay have weight average molecular weights Mw of from about 3 000 to 300000, which can be determined by conventional methods.

Examples of suitable comonomers for the preparation of copolymers are(meth)acrylic acid, alkyl (meth)acrylates where the alkyl radical is offrom 1 to 4 carbon atoms, acrylonitrile and maleic anhydride andmaleimides, acrylamide and methacrylamides and their N,N- andN-alkyl-substituted derivatives where the alkyl radical is of 1 to 10carbon atoms. Suitable examples of such C₁₋₁₀-alkyl groups includemethyl, ethyl, n-propyl and isopropyl, n-butyl, tert-butyl andstraight-chain and branched pentyl, hexyl, heptyl, octyl, nonyl anddecyl. Depending on their chemical structure, the comonomers arecontained in the styrene polymers in different amounts. Miscibility ofthe copolymer with the polyphenylene ether is decisive with regard tothe content of comonomers in the copolymer. Such miscibility limits areknown and are described, for example, in U.S. Pat. Nos. 4,360,618, and4,405,753 and in the publication by J. R. Fried and G. A. Hanna, PolymerEng. Scie., 22 (1982), 705 et seq. The copolymers are prepared by knownprocesses which are described, for example, in Ullmanns Enzyklopadie dertechn. Chemie, Volume 19, page 273 et seq., Verlag Chemie, Weinheim(1980). The copolymers generally have a weight average molecular weight(M_(w)) of from about 10 000 to about 300 000, which can be determinedby conventional methods.

According to the invention, high-impact polystyrene is preferably usedas component B.

The generally used processes for the preparation of high-impact styrenepolymers are mass and solution polymerization in the presence of arubber, as described, for example, in U.S. Pat. No. 2,694,692, andprocesses for mass-suspension polymerization as described, for example,in U.S. Pat. No. 2,862,906. Other processes can of course also be used,provided that the desired particle size of the rubber phase isestablished.

The novel molding materials contain, as flameproofing agent (componentC), from about 1 to about 20, preferably from about 2 to about 19, inparticular from about 2.5 to about 18,% by weight, based on the totalweight of said molding materials, of a flameproofing combinationcomprising

C₁: from about 5 to about 95% by weight of a phosphorus compound of theabove general formula (I) and/or of the formula (II) and

C₂: from about 5 to about 95% by weight of a phosphine oxide of thegeneral formula (III), the stated percentages by weight for C₁ and C₂each being based on the total weight of component C.

Examples of phosphine oxides (component C₂) are triphenylphosphineoxide, tritolylphosphine oxide, trisnonylphenylphosphine oxide,tricyclohexylphosphine oxide, tris-(n-butyl)phosphine oxide,tris-(n-hexyl)phosphin oxide, tris-(n-octyl)phosphine oxide,tris-(cyanoethyl)phosphine oxide, benzylbis(cyclohexyl)phosphine oxide,benzylbisphenylphosphine oxide and phenylbis-(n-hexyl)phosphine oxide.Triphenylphosphine oxide, tricyclohexylphosphine oxide,tris-(n-octyl)phosphine oxide and tris-(cyanoethyl)phosphine oxide areparticularly preferably used.

Oligophosphorus compounds suitable according to the invention areobtainable, for example, by reacting bisphenols with triphenylphosphate. Examples of oligophosphorus compounds (component C₁) areresorcinol diphenyl phosphate and hydroquinone diphenyl phosphate.According to the invention oligophosphorus compounds based on bisphenolA or bisphenol S may also be used.

It should be noted that the industrially available products C₁ are ineach case mixtures of different oligomers or isomers.

Rubber impact modifiers are used as impact modifiers (component D) inamounts of up to about 50, preferably up to about 25, in particular upto about 20,% by weight, based on the total weight of the material.

Natural or synthetic rubbers may be used as component D. In addition tonatural rubber, suitable impact modifiers are, for example,polybutadiene, polyisoprene or copolymers of butadiene and/or isoprenewith styrene and other comonomers, which have a glass transitiontemperature of from about −100° C. to +25° C., preferably less than 0°C., determined according to K. H. Illers and H. Breuer,Kolloidzeitschrift 190 (1), 16-34 (1963). Appropriately hydrogenatedproducts may also be used.

Preferred impact modifiers D are block polymers of vinyl aromatics anddienes. Impact modifiers of this type are known. German PublishedApplications DAS 1,932,234, and DAS 2,000,118 and German Laid-OpenApplication DOS 2,255,930 describe elastomeric block copolymers havingdifferent compositions and comprising vinyl aromatic and diene blocks.The use of appropriately hydrogenated block copolymers, if necessary asa mixture with the unhydrogenated precursor, as impact modifiers isdescribed, for example, in German Laid-Open Applications DOS 2,750,515,DOS 2,434,848 and DOS 3,038,551, EP-A-0 080 666 and WO 83/01254. Thedisclosure of the above publications is hereby incorporated byreference.

In particular, vinyl aromatic diene block copolymers comprising blockswhich have a hard phase (block type S) and, as the soft phase, a randomB/S block comprising diene and vinyl aromatic units may be usedaccording to the invention. The composition may on statistical averagebe homogeneous or inhomogeneous along the chain.

Such an elastomeric block copolymer suitable according to the inventionis obtained by forming the soft phase from a random copolymer of a vinylaromatic with a diene; random copolymers of vinyl aromatics and dienesare obtained by polymerization in the presence of a polar cosolvent.

A block copolymer which may be used according to the invention can berepresented, for example, by one of the following general formulae (1)to (11):

(S—B/S)_(n);  (1)

(S—B/S)_(n)—S;  (2)

B/S—(S—B/S)_(n);  (3)

X—[(S—B/S)_(n)]_(m)+1  (4)

X—[(B/S—S)_(n)]_(m)+1;  (5)

X—[(S—B/S)_(n)—S]_(m+);  (6)

X—[(B/S—S)_(n)—B/S]_(m)+1;  (7)

Y—[(S—B/S)_(n)]_(m+)1;  (8)

Y—[(B/S—S)_(n)]_(m)+1;  (9)

Y—[(S—B/S)_(n)—S]_(m)+1;  (10)

Y—[(B/S—S)_(n)—B/S]_(m)+1;  (11)

where

S is a vinyl aromatic block,

40 B/S is the soft phase comprising a random block of diene and vinylaromatic units,

X is a radical of an n-functional initiator,

Y is a radical of an m-functional coupling agent and

m,n are natural numbers from 1 to 10.

A block copolymer of one of the general formulae S—B/S—S, X—[—B/S—S]₂and Y—[—B/S—S]₂ (meanings of the abbreviations as above) is preferred,and a block copolymer whose soft phase is divided into blocks

(B/S)₁—(B/S)₂;  (12)

(B/S)₁—(B/S)₂—(B/S)₁;  (13)

(B/S)₁—(B/S)₂—(B/S)₃;  (14)

where the indices 1, 2 and 3 represent different structures by virtue ofthe fact that the vinyl aromatic/diene ratio differs in the individualblocks B/S or changes continuously within the limits (B/S)₁(B/S)₂ withina block, the glass transition temperature T_(g) of each part-block beingless than 25° C, is particularly preferred.

A block copolymer which has a plurality of blocks B/S and/or S withdifferent molar mass per molecule is also preferred.

A block S which is composed exclusively of vinyl aromatic units mayfurthermore be replaced by a block B since all that is important overallis that an elastomeric block copolymer is formed. Such copolymers mayhave, for example, one of the structures (15) to (18)

B—(B/S)   (15)

B/S)—B—(B/S)  (16)

B/S)₁—B—(B/S)₂  (17)

B—(B/S)₁—(B/S)₂.  (18)

Preferred vinyl aromatics are styrene, o-methylstyrene, vinyltoluene andmixtures of these compounds. Preferred dienes are butadiene, isoprene,piperylene, 1-phenylbutadiene and mixtures of these compounds. Aparticularly preferred monomer combination comprises butadiene andstyrene.

The soft blocks are particularly preferably composed of from about 25 to75% by weight of styrene and from about 25 to 75% by weight ofbutadiene. Soft blocks which have a butadiene content of from about 34to 69% by weight and a styrene content of from about 31 to 66% by weightare particularly preferred.

The amount by weight of the diene in the total block copolymer in thecase of the styrene/butadiene monomer combination is from 15 to 65% byweight, and that of the vinyl aromatic component is accordingly from 85to 35% by weight. Butadiene/styrene block copolymers having a monomercomposition comprising from 25 to 60% by weight of diene and from 75 to40% by weight of vinyl aromatic compound are particularly preferred.

The block copolymers are obtainable by anionic polymerization in anunpolar solvent with the addition of a polar cosolvent. It is thoughtthat the cosolvent acts as a Lewis base with respect to the metalcation. Preferably used solvents are aliphatic hydrocarbons, such ascyclohexane and methylcyclohexane. Preferred Lewis bases are polaraprotic compounds such as ethers and tertiary amines. Examples ofparticularly effective ethers are tetrahydrofuran and aliphaticpolyethers, such as diethylene glycol dimethyl ether. Examples oftertiary amines are tributylamine and pyridine. The polar cosolvent isadded to the nonpolar solvent in a small amount, for example from 0.5 to5% by volume. Tetrahydrofuran in an amount of from 0.1 to 0.3% by volumeis particularly preferred. Experience has shown that an amount of about0.2% by volume is sufficient in most cases.

The copolymerization temperature and the proportion of 1,2 and 1,4linkages of the diene units are determined by the dose and structure ofthe Lewis base. The novel polymers contain, for example, from 15 to 40%of 1,2 linkages and from 85 to 60% of 1,4 linkages, based on all dieneunits.

The anionic polymerization is initiated by means of organometalliccompounds. Compounds of the alkali metals, in particular of lithium, arepreferred. Examples of initiatiors are methyllithium, ethyllithium,propyllithium, n-butyllithium, sec-butyllithium and tert-butyllithium.The organometallic compound is added as a solution in a chemically inerthydrocarbon. The dose depends on the desired molecular weight of thepolymer but is as a rule from 0.002 to 5 mol %, based on the monomers.

The polymerization temperature may be from about 0 to 1300C, preferablyfrom 30 to 100° C.

The volume fraction of the soft phase in the solid is of decisiveimportance for the mechanical properties. According to the invention,the volume fraction of the soft phase composed of diene and vinylaromatic sequences is from 60 to 95, preferably from 70 to 90,particularly preferably from 80 to 90,% by volume. The blocks A formedfrom the vinyl aromatic monomers form the hard phase, their volumefraction being accordingly from 1 to 40, preferably from 10 to 30,particularly preferably from 10 to 20,% by volume.

It should be pointed out that there is no strict agreement 5 between theabovementioned ratios of vinyl aromatic compound and diene, theabovementioned limits of the phase volumes and the composition whicharises out of the novel ranges of the glass transition temperature, asthey are in each case numerical values rounded to full tens. Rather, anyagreement might be merely accidental.

The volume fraction of the two phases can be measured by means ofhigh-contrast electronmicroscopy or solid-state NMR spectroscopy. Theamount of the vinyl aromatic blocks can be determined by osmiumdegradation of the polydiene content by precipitation and weighing. Thefuture phase ratio of a polymer can also be calculated from the amountsof monomers used, if polymerization is allowed to go to completion eachtime.

The block copolymer is uniquely defined for the purposes of the presentinvention by the quotients of the volume fraction as a percentage of thesoft phase formed from the B/S blocks and the proportion of diene unitsin the soft phase, which is from 25 to 70% by weight for thestyrene/butadiene combination.

The glass transition temperature (Tg) is influenced by the randomincorporation of the vinyl aromatic compounds in the soft block of theblock copolymer and the use of Lewis bases during the polymerization.The glass transition temperature of the total copoylmer is preferablyfrom −50° C. to +25° C., particularly preferably less than 0° C.

The molecular weight of the S block is preferably from 1000 to 200000,in particular from 3000 to 80000 [g/mol]. Within a molecule, S blocksmay have different molar masses.

The molecular weight of the B/S block is usually from 2000 to 250000,preferably from 5000 to 150000 [g/mol].

As in the case of block S, block B/S too, may assume different molecularweights within a molecule.

The coupling center X is formed by reacting the living anionic chainends with a bifunctional or polyfunctional coupling agent. Examples ofsuch compounds are to be found in U.S. Pat. Nos. 3,985,830, 3,280,084,3,637,554 and 4,091,053. For example, epoxidized glycerides, such asepoxidized linseed oil or soya bean oil, are preferably used;divinylbenzene is also suitable. Dichlorodialkylsilanes, dialdehydes,such as terephthalaldehyde, and esters, such as ethyl formate orbenzoate, are particularly suitable for the dimerization.

Preferred polymer structures are S—B/S—S, X—[—B/S—S]₂ and Y—[—B/S—S]₂,where the random block B/s it self in turn may be subdivided into blocksB1/S1-B2/S2-B3/S3- . . . . The random block preferably consists of from2 to 15, particularly preferably from 3 to 10, random part-blocks. Thedivision of the random block B/S into a very large number of part-blocksBn/Sn offers the decisive advantage that the B/S block as a wholebehaves like a virtually perfect random polymer even in the case of acomposition gradient within a part-block Bn/Sn as can be avoided onlywith difficulty in the anionic polymerization under practicalconditions. It is therefore possible to add less than the theoreticalamount of Lewis base, which increases the proportion of 1,4-dienelinkages, lowers the glass transition temperature Tg and reduces thesusceptibility of the polymer to crosslinking. A larger or smalleramount of the part-blocks can be provided with a high diene content.This results in the polymer retaining a residual toughness and notbecoming completely brittle even below the glass transition temperatureof the predominant B/S blocks.

All the abovementioned weights and volumes are based on thebutadiene/styrene monomer combination. However, these data can bereadily converted to other monomers technically equivalent to styreneand butadiene.

Block copolymers can be worked up by protonating the carbanions with analcohol, such as isopropanol, acidifying the reaction mixture, forexample with a mixture of CO₂ and water, and removing the solvent. Theblock copolymers may contain antioxidants and antiblocking agents.

From about 0 to 10, in particular from about 0.5 to 5% by weight ofhydroxyl-containing polymers of the type comprising the condensates ofbisphenols and epichlorohydrin may be used as the polymeric hydroxycompound (component E) in the thermoplastic molding materials. Examplesof suitable bisphenols are bisphenol A, B, C, F, S and Z. See alsoUllmann's Encyclopedia of Industrial Chemistry, fifth edition, Vol. A19, p. 349. The condensate of bisphenol A and epichlorohydrin which issold under the trade name Phenoxy®PKH is preferably used. Thehydroxyl-containing compound is furthermore characterized by a viscositynumber of from about 20 to 80 ml/g (measured in 0.5% strength CH₂Cl₂solution at 25° C.).

The novel molding materials may also contain conventional additives andprocessing assistants as component F). The amount of these additives isin general not more than about 60, preferably not more than about 50, inparticular not more than about 30,% by weight, based on the total weightof the components A) to D).

Examples of additives are heat stabilizers, light stabilizers,lubricants, mold release agents and colorants, such as dyes andpigments, in conventional amounts. Further additives are reinforcingagents, such as glass fibers, carbon fibers, aromatic polyamide fibers,and/or fillers, gypsum fibers, synthetic calcium silicates, kaolin,calcinated kaolin, wool astonite, talc and chalk.

Furthermore, lubricants, such as polyethylene wax, are suitableadditives.

Carbon blacks and titanium dioxide may be used, for example, aspigments.

When TiO₂ is used, the mean particle size is as a rule from about 50 to400 nm, in particular from about 150 to 240 nm. Rutile and anatase,which if required are coated with metal oxides, e.g. aluminas, silicasor oxides of zinc and siloxanes, are used industrially.

Carbon blacks are to be understood as meaning microcrystalline, finelydivided carbons (cf. Kunststofflexikon, 7th edition 1980).

Suitable examples are furnace blacks, acetylene blacks, gas blacks andthe thermal blacks obtainable by thermal preparation.

The particle sizes are preferably from about 0.01 to 0.1 μm and thesurface areas are from about 10² to 10⁴ m²/g (BET/ASTM D 3037) and fromabout 10² to 10³ ml/100 g in the case of DBP absorptions (ASTM D 2414).

The novel molding materials are advantageously prepared by mixing thecomponents at from about 230 to 320° C. in a conventional mixingapparatus, such as a kneader, Banbury mixer or single-screw extruder,preferably in a twin-screw extruder. Thorough mixing is necessary forobtaining a very homogeneous molding material. The order in which thecomponents are mixed may be varied; two components or, if required, aplurality of components may be premixed or all components may be mixedtogether.

The novel molding materials are very suitable for the production ofshaped articles of all types. They can furthermore be used for theproduction of films and semi-finished products by the deep drawing orblow molding method.

Owing to their very good flowability and processing stability, the novelmolding materials can be converted, for example by injection molding orextrusion, into moldings which are flame-retardant and have excellentmechanical properties.

The examples which follow illustrate the invention

EXAMPLES

The novel molding materials 1 to 4 are prepared using the components A)to E) listed below and their properties are compared with those of thecomparative molding materials V1, V2 and V3.

Component A)

Poly-2,6-dimethyl-1,4-phenylene ether having an average molecular weight(M_(w)) of 40000 g/mol.

Component B₁)

High impact polystyrene containing 9% by weight of polybutadiene andhaving a cellular particle morphology, mean particle size of the softcomponent of 1 μm. The VN of the hard matrix was 80 ml/g (0.5% strengthin toluene at 23° C.).

Component B₂)

High impact polystyrene containing 9% by weight of polybutadiene andhaving a cellular particle morphology, mean particle size of the softcomponent of 5 μm. The VN of the matrix was 80 ml/g (0.5 % strength intoluene at 23° C.).

Component C₁)

Resorcinol diphenyl phosphate, commercial product Fyrolflex RDP (Akzo).

Component C₂)

Triphenylphosphine oxide

Triphenylphosphate (TPPA) was used for comparative experiments.

Component D)

SEPS block rubber, e.g. Kraton G 1650 (Shell AG).

Componente E)

Phenoxy PKH

Preparation of thermoplastic molding materials

The components A) to E) were mixed in a twin-screw extruder (ZSK fromWerner & Pfleiderer) at 270° C. and the mixture was extruded, cooled andgranulated.

Determination of the properties of thermoplastic molding materials

The dried granules were processed at from 250 to 280° C. to givecircular disks, flat bars for the UL 94 test and standard small bars.The damaging energy W_(s) was determined according to DIN 53 443 at 230°C.

The heat distortion resistance of the samples was determined by means ofthe Vicat softening temperature, measured according to DIN 53 460, witha force of 49.05 N and a temperature increase of 50 K per hour, usingstandard small bars.

The flame retardance was determined according to UL 94 using {fraction(1/16)}″, thick bars; the combustion times mentioned are the sum of thecombustion times of the two flame applications.

The flowability of the molding materials (shearing stability) wasdetermined from the percentage changes in the torque (ΔD) duringkneading of the materials in a kneader of the type Haake Theomix 600,the torque after 6 and 26 minutes being compared (kneader temperature275° C.).

The flowability of the samples was evaluated using the MVI value (DIN53735) the measurements being carried out at a melt temperature of 275°C. and under a load of 21.6 kg.

The composition and properties of the thermoplastic molding materialsprepared are listed in Table 1.

TABLE 1 Component Molding material No. (% by weight) V1 V2 V3 1 2 3 4 A52 52 52 52 52 52 52 B₁ 32 32 32 32.5 30.5 31 31 B₂ — — — — 2 2 2 C₁ —13 6.5 6.5 6.5 8 8 C₂ 6.5 — — 6.0 6.0 4 3.5 D 3 3 3 3 3 3 3 TPPA 6.5 —6.5 — — — — E — — — — — — 0.5 W_(s) [Nm] 42 32 39 43 47 46 44 Vicat B [°C.] 111 114 112 113 112 115 115 UL 94 V-0 V-1 V-0 V-0 V-0 V-0 V-0Combustion time 45 66 46 32 33 42 21 [s] MVI [ml/10′] 125 89 103 112 111106 113 ΔD (%) 26 4 17 9 9 6 5 The results of the measurementsdemonstrate a surprisingly improved property profile for the novelmolding materials 1 to 4.

We claim:
 1. A flame-retardant thermoplastic molding material containingA) at least one polyphenylene ether and B) at least one vinyl aromaticpolymer, which comprises, C) as a flameproofing agent, a mixture of C₁)at least one oligophosphorus compound selected from compounds of theformula (I) or (II)

where R¹ and R⁴, independently of one another, are each unsubstituted orsubstituted alkyl or aryl, R² and R³, independently of one another, areeach unsubstituted or substituted alkyl, aryl, alkoxy or aryloxy, R⁵ isalkylene, —SO₂—, —CO—, —N═N— or —(R⁶)P(O)—, where R⁶ is unsubstituted orsubstituted alkyl, aryl or alkylaryl, and n and p, independently of oneanother, are each from 1.0 to 30, and C₂) at least one phosphine oxideof the formula (III)

where R⁷, R⁸ and R⁹, independently of one another, are each hydrogen orunsubstituted or substituted alkyl, aryl, alkylaryl or cycloalkyl of upto 40 carbon atoms.
 2. A molding material as claimed in claim 1, whichcontains the flameproofing mixture in an amount of from about 1 to about20% by weight based on the total weight of the material.
 3. A moldingmaterial as claimed in claim 1, which contains at least one polymerichydroxy compound in an amount which improves the combustion behavior. 4.A molding material as claimed in claim 1, containing A) from about 5 toabout 98% by weight of at least one polyphenylene ether, B) from about 1to about 94% by weight of at least one styrene polymer, C) from about 1to about 20% by weight of a flameproofing combination which comprises,from about 5 to about 95% by weight, based on the weight of theflameproofing combination, of at least one oligophosphorus compound ofthe above formula (I) or (II) as component C₁ and from about 5 to about95% by weight, based on the weight of the flameproofing combination, ofa phosphine oxide of the above formula (III) as component C₂; D) from 0to about 50% by weight of at least one impact modifier, E) from 0 toabout 10% by weight of a hydroxyl-carrying polymer and F) from 0 toabout 60% by weight of at least one conventional additive.
 5. A moldingmaterial as claimed in claim 4, which contains, as the flameproofingcombination, a mixture of resorcinol diphenyl phosphate or hydroquinonediphenyl phosphate with triphenylphosphine oxide.
 6. A molding materialas claimed in claim 1, wherein the oligophosphorus compound andphosphine oxide are present in a molar ratio of from about 1:9 to about9:1.
 7. A molding material as claimed in claim 3, which contains fromabout 0.5 to about 5% by weight of the hydroxy groups carrying polymericcompound.
 8. A molding material as claimed in claim 3, wherein thehydroxy groups carrying polymer compound is the reaction product of abisphenol and epichlorhydrin.
 9. A flame-retardant molding, fiber orfilm, produced using a 20 molding material as claimed in claim
 1. 10. Acombination of flame-retardants, comprising a combination of at leastone oligophosphorus compound, selected from compounds of the generalformula (I) and (II)

where R¹ and R⁴, independently of one another, are each unsubstituted orsubstituted alkyl, or aryl, R²and R³, independently of one another, areeach unsubstituted or substituted alkyl, aryl, alkoxy or aryloxy, R⁵ isalkylene, —SO₂—, —CO—, —N═N— or —(R⁶)P(O)—, where R⁶ is unsubstituted orsubstituted alkyl, aryl or alkylaryl, and n and p, independently of oneanother, are each from 1.0 to 30, and at least one phosphine oxide ofthe general formula (III)

where R⁷, R⁸ and R⁹ independently of one another, are each hydrogen orunsustituted or substituted alkyl, aryl, alkylaryl or cycloalkyl of upto 40 carbon atoms.
 11. A combination of flame-retardants of claim 10,containing the oligophosphorous compound and the phosphine oxide in amolar ratio of about 1:9 to about 9:1.